Method of simultaneously coating the opposite sides of a paper web

ABSTRACT

A method for simultaneously coating the opposite sides of a paper web which involves employing an opposed blade coating system. Wet coating material is applied to the opposite sides of the web, the wet coated web is passed through the nip of a flexible blade unit comprised of a pair of blades having flat bevelled working surfaces engaging opposite sides of the coated web in opposed relationship with each other for metering the layer of coating on the opposite sides of the web, and thereafter the coated web is dried.

0 United States Patent 11 1 1111 3,889,018 Quint 1 June 10, 1975 [54]METHOD OF SIMULTANEOUSLY 3,001,219 9/1961 Miller 15/245 COATING THEOPPOSITE SIDES OF A g a 1 1 1 rown eta. l3 PAPER WEB 3,078,825 2/1963Munton et a1.. 118/413 [75] Inventor: Richard J. Quint, Dixfield, Maine3,119,138 11/1964 Davis 15/245 3,187,718 6/1965 COghill..... 118/126[73] Ass1gnee: Ethyl Corporation, R1chmond, \la. 3,190,263 6/1965 Bslaku [18/101 22 d: A 1, 3,230,928 Stalmuke 1 3,241,521 3/1966 Labombarde...118 122 [21] Appl. No.: 384,689 3,251,339 5/1966 Whitfield 118/1223,260,577 7/1966 Mayhew 29/1835 Related Appllcamn Data 3,477,149 11/1969Wagner 15 245 [60] Division of Ser, No. 341,928, March 16, 1973, which3,489,592 11/1970 wallsten 117/68 is a continuation of Ser. No. 82,475,Oct, 20, 1970, 3,575,134 4/1971 Quint 118/122 abandoned, which is adivision of Ser. No. 703,924,

Feb. 8, 1968.

52 us. c1. 427/209; 118/122; 427/356 51 161.0. B056 11/02 [58] Field 61Search..... 117/68, 68.5, 102 L, 111 R,

References Cited UNITED STATES PATENTS Jones 117/64 Seidell et a1.118/122 Charch et a1. 118/65 Boyer et a1. 117/111 Forse 118/103 Nokes118/121 Kierspe 118/122 Friedman 118/122 Knight ct a1. 118/68 Slavin15/245 Brough 1 15/245 Faulkner.... 118/121 Paquette 118/405 Wolfe etal. 117/68 Oganowski 117/68 FOREIGN PATENTS OR APPLICATIONS 498,002 12/1938 United Kingdom 548,632 lO/l942 United Kingdom 741,371 11/1955United Kingdom 7 639,538 12/1936 Germany 1,224,601 9/ 1 966 GermanyPrimary ExaminerMichacl Sofocleous Attorney, Agent, or Firm-Donald L.Johnson; John F. Sieberth [5 7] ABSTRACT A method for simultaneouslycoating the opposite sides of a paper web which involves employing anopposed blade coating system. Wet coating material is applied to theopposite sides of the web, the wet coated web is passed through the nipof a flexible blade unit comprised of a pair of blades having flatbevelled working surfaces engaging opposite sides of the coated web inopposed relationship with each other for metering the layer of coatingon the opposite sides of the web, and thereafter the coated web isdried.

14 Claims, 6 Drawing Figures PATENTED JUH l 0 I975 SHEET I'll L IWUSHEET PATENTED JUN 10 I975 PATENTEDJUH I 0 I975 SHEET INCREASINGPRESSURE METHOD OF SIMULTANEOUSLY COATING THE OPPOSITE SIDES OF A PAPERWEB REFERENCE TO RELATED APPLICATIONS This is a division of my priorcopending application Ser. No. 341,928 filed Mar. 16, 1973, which is acontinuation of application Ser. No. 82,475 filed Oct. 20, 1970 and nowabandoned. which in turn is a division of application Ser. No. 703,924filed Feb. 8, 1968. now US. Pat. No. 3,575,134.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionpertains to paper web coating systems and more particularly to a coatingsystem for simultaneously coating the opposite sides of the paper web.

2. Description of the Prior Art In the production of paper, it isoftendesirable to apply a coating to the opposite sides of the paperwhen it is in web form and before cutting into sheets. Different typesof coating apparatus are available for producing such coated web;however, presently available equipment is not altogether satisfactory asfar as efficiency and versatility of the machinery and the quality ofthe coated paper is concerned. A primary source of difficulty inobtaining quality coated paper with presently available equipmentresides in the mechanism used for doctoring the layer of coating asapplied to the paper. Desirably, the coating on the final product shouldcompletely cover the paper fibers on both sides of the web and beuniform in thickness and coat weight throughout. Also, depending on thetype of base sheet being run through the coating apparatus and theparticular characteristics desired in the final product, differentcoating materials having varying properties will be required. Withpresently available coating apparatus, the conventionally constructeddoctoring mechanisms impose various limitations on both the operatingversatility and efficiency of the equipment and the products which it iscapable of producing.

In the typical size press, for example, the thickness of the coating iscontrolled by passing the web between a pair of rotating doctor rolls.These rolls, which are relatively large in size so as to withstand thepressure created and to present an even nip for the incoming paper,create certain forces acting on the liquid coating material tending todisrupt the evenness of the final coating on the web. More particularly,the coating tends to neck down and stay with the rolls as the web exitstherefrom to produce what is called a film split pattern. This action ismore prevalent when higher coat weights are applied to the web; and inorder to produce a quality coating of the web, the coat weight of thecoating has to be kept relatively low. As a practical matter, these coatweights are not greater than 4 or 5 pounds per ream on each side of thepaper; with attempts to attain higher coat weights resulting inunacceptable coatings having uneven thickness and surface patterns. Evenwith these coat weights of 4 to 5 pounds, some substantial amount of thecoating material on the final product will be impregnated into the paperrather than adhered to its surfaces. This is due to the pressure createdon the coated paper by the doctor rolls. Because of this, coated paperproduced in a size press will not be of the same high quality as wouldbe a coated'paper with the same coat weight but with the coatingmaterial substantially all adhered to the surfaces of the paper,

Also, because of the large size of the doctor rolls typically employedin a size press, the speed at which these rolls are driven and thus, thespeed atwhich the web can be fed through the machinery is limited. In aconventional size press, the maximum acceptable speed of the web isabout 1200 ft. per minute. Higher speeds of the web create problems inproperly applying the coating to the web, with the doctor rolls tendingto cause splattering of the coating material.

In addition to these limitations as to coat weight and web speed, sizepress units are usually best suited for coating paper webs with coatingmaterials having no more than about 45% solids content. With highersolids content, more undesirable coating patterns are produced on thefinal product. The above-discussed operating characteristics of theconventional size press limit its versatility and thus the variety ofcoated paper products capable of being produced thereby.

In the conventional blade coating apparatus employing a steel doctorblade for scraping off excess coating, the coating of the opposite sidesof the web iseffected in two successive single coating operations. This,in turn, requires that the web be dried after the first coatingoperation, before the web is coated on its other side, and then driedagain after the second coating operation and before the web is furtherprocessed. This not only affects the ultimate cost of the finishedproduct due to the very nature of the coating process; but also requiresthat considerable area be provided for installation of the necessaryequipment. Also, the operating versatility of such'equipment is notcompletely satisfactory. For'example, such equipment is only suited foroperating at web speeds above 600 to 800 ft. per minute and usually atspeeds above 1,000 ft. per minute. In some coating applications,however, it is desirable to run the web through the coater at speedsbelow these values. These lower speeds may, for example, be founddesirable with certaincoating materials in order to produce qualitycoating. With the conventional blade coating apparatus using a steeltrailing blade, speeds'much lower than 1,000 ft. per minute result inlower quality than that obtained at speeds over 1,000 ft. per minutesince at these lower speeds, the conventional blade coater cannoteffectively control the coat weight of the coating.

SUMMARY OF THE INVENTION In accordance with the teachings of the presentinvention, there is provided a coating apparatus having a wideroperating range than conventional devices. More particularly, withapplicants coating system, web speeds in excess of 1,400 ft. per minuteand web speeds below 600 ft. per minute may be used to thus permit theselection of a wider range of base sheets and coating materials. Inaddition, generally higher coat weights may be applied to opposite sidesof the web than with conventional equipment, and coating materialshaving a wider range of solids content of pigment and adhesive may beused. For example, higher coat weights may be applied at lower solidscontent than is possible with conventional coating apparatus. By beingable to use coating materials having varying characteristics andproperties and by being able to selectively change the operatingconditions of the coater, a wider range of high quality coated productscan be produced.

Generally, the coating apparatus employed with applicant's coatingsystem includes suitable means for applying a layer of coating to theopposite sides of the web, feeding means for feeding the coated web awayfrom the coating station and through a metering station, and a dryingstation through which the web is then fed to dry the coating. In themetering station, there is provided a pair of metering blades engagingagainst the opposite sides of the coated web; and in accordance with theteachings of the present invention, these metering blades areconstructed of flexible material and are each provided with a flatbevelled working surface for engagement with the coated web. The bladesthemselves extend freely from a support means on opposite sides of theweb and at an acute angle relative to the movement ofthe webtherebetween. This angle of extension or head angle of the blades andthe angle of bevel of the individual blades is so chosen thatpositioning of the blades in opposed relationship with each other willcause their bevelled working surfaces to oppose each other and establishat least a partially flush engagement along their bevelled surfaces withthe opposite sides of the coated web.

As compared to conventional coating apparatus where the doctoringmechanisms have a more or less line contact or at best a very limitedarea of contact with the coated web, the flat bevelled working surfacesof the opposed metering blades of the present invention engage againstthe opposite sides of the coated paper over a substantial area thusdecreasing the pressure needed to effect a proper control of the coatingapplication. Accordingly, the opposed blades of the present inventionfunction to actually meter and smooth the layer of coating applied tothe opposite sides of the paper rather than to merely remove excesscoating with a scraping action. In addition, the construction andorientation of the opposed blades are such as to minimize wearingthereof and thereby increase their operating life to about four timesthat of the steel doctor blades used in conventional blade coatingapparatus. Also, with the present invention, the coating isadvantageously applied to the opposite surfaces of the paper without theundesirable impregnation of the coating material into the paper asoccurs with conventional coating apparatus.

Generally, a higher quality coated paper can be produced with thecoating system of the present invention; and by controlling suchvariables as the amount of extension and the angle of extension of theblades and by using blades having different flexing characteristics andbevelled working surfaces and by varying the pressure urging the bladesagainst the opposite sides of the web, a wide variety of high qualitycoated paper may be produced under selected operating conditions of theapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of theimproved coating system of the present invention;

FIG. 2 is an enlarged view of the opposed blade doctor mechanism shownin FIG. 1;

FIG. 3 is a cross-sectional view of one of the doctor blades shown inFIG. 2;

FIG. 4 is an enlarged view ofa pair of opposed doctor blades of thepresent invention showing their relative positioning with respect to thecoated web;

FIG. 5 is a cross-sectional view of the blade holder shown in FIG. 2;and

FIG. 6 is a graph representing the affect of certain variables on thecoat weight of the coated paper produced with the coating system of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. I, the coatingapparatus of the present invention generally includes a coating stationI having a pair of applicator rolls 2 for applying coating material toopposite sides of the web being fed therebetween. The rolls 2 arerotatably mounted in associated troughs 3 in which the coating materialto be applied to the web is contained. The web of paper to be coated,designated at 4, is supplied from a supply roll 5 rotatably mounted onsuitable means, not shown. As the web is fed from the supply roll, it isinitially directed around a guide roll 6 and fed in an upward, verticaldirection through the coating station. A metering station 7 is disposedabove the coating station 1; and above this, there is a drying station 8having suitable drying devices such as infrared burner units 9 and steamcan dryers, one of which is shown at 9'. For feeding the web through thecoating apparatus, the steam can dryers are advantageously driven by asuitable motor, not shown.

In accordance with the teachings of the present invention, an improvedmetering mechanism is provided for metering the coating material appliedto the web. As most clearly seen from FIG. 2, the improved meteringmechanism of the present invention is constructed for operation undervarious positions of adjustment. More particularly, this mechanismincludes a pair of opposed metering blades 10 for engaging against theopposite sides of the coated web, blade holders 11 for clamping theblades at a point rearwardly of their free working ends, slidablecarriages 12 for mounting the blade holders in selected angularpositions, and pneumatic piston-cylinder units 13 for urging themetering blades into selected opposed engagement with the coated web.

The presently preferred blade holders 11, one of which is shown in FIG.5, include opposed clamping members 14, 15 extending the length of theblades across the web to be coated. The clamping members provide ahollow interior in which a blade cartridge 16 is removably disposed; andthe cartridge itself is constructed of two halves removably connectedtogether by suitable means (not shown) for holding the blade 10 therein.In order to assure an accurate, parallel alignment of the blades 10 withthe coated web and to compensate for any irregularities in thisalignment that may be caused due to theclamping members, the blades 10are resiliently rather than rigidly mounted in their associatedcartridges and in spaced relationship relative to the walls 14' and 15'of the clamping members 14 and 15. In the presently preferredconstruction, the resilient mounting of the blade within the clampingmembers and cartridge is accomplished by providing an insert 17 of thesame flexible material as is used for the blade; this insert beingpositioned on the side of the blade facing the coated web to be metered.Therefore, upon engagement of the blade with the coated side of the weband flexing thereof as more fully described below, the rear end of theblade will tend to become bowed into the flexible insert and the surfaceof the blade facing away from the coated web will move into non-rigidengagement with the edge of the blade clamping member at the outerextent of its wall surface 15. With this construction, the opposedblades willpresent substantially parallel surfaces engaging oppositesides of the coated web and thereby produce an even metering andsmoothing of the coating on the paper.

A further advantage of the blade holder as shown in FIG. 5 resides inthe construction of the cartridge unit 16. As indicated above, thecartridge is'removably positioned in the hollow interior of the clampingmembers. Thus, the bladesmay be secured to the cartridge at a pointremote from the coating apparatus and be ready for quick placementwithin the clamping members when it is desired to change blades becauseof wear or to substitute a'blade of differentconstruction for aparticular coating operation. In addition, the cartridge-is providedwith a plurality'ofshims 18, 18' at the ends of the insert with theshims l8 supporting'the rear end of the blade. With this construction, ablade having a worn working surface'may be reground and reinserted intothe cartridge with the same length of extension from the blade clampingmembers as the length of extension of the original, new bladel This isreadily efsetting for the blades has been determined, these stops may bepositioned in the appropriate location along the tracks 24 to accuratelyalign the blades relative to the path of movement of the web through themetering station.

In accordance with the teachings of the present invention, the meteringblades 10 are constructed of flexible material. A material foundadmirably suited for this purpose is polyurethane such as thatmanufactured under the tradename ISOTHANE by The Carborundum Company.This material is of medium softness having a durometer hardness of 95Shore A and a P and J (Pusey and Jones) plastometer value of 20. Otherpolyurethanes such as the harder polyurethane having a durometerhardness of 70 Shore Dand a P and J plastometer value of 4 and thesofter polyurethane having a durometer hardness of 90 Shore A and a Pand J plastometer value of 27 have also been found suitable especiallywhere one of these blades is used in combination with a polyurethaneblade of medium softness. Further properties of these polyurethanes areset out in Table I, below.

TABLE I Specifications of Polyurethane Material fected by removing oneormore of the shims 18 and adding a corresponding number of shims 18' ofthe same thickness. Also, the inclusion of these shins l8, 18 provides aconvenient means by which the blade extension of any blade, new orreground, may be adjusted accurately within a limited range.

For permitting adjustment of the angle of extension or head angle of theopposed blades relative to the web passing through the metering station,the base of each blade holder 11 is rotatably secured to a support shaft19 about which it may be rotated. The angular position ofthe bladeholders is controlled by a pairof adjusting screws 20, each of which ispivoted to an upstanding support assembly 21 of one of the carriages l2and threadedly received through an arm member 22 fixed to the base ofthe blade holder associated with the carriage. Accordingly, rotation ofthe screws will cause an angular adjustment of the blade holders; andfor indicating the angle of extension at which the blades-are set,suitable scales 23 are provided.

For setting the metering blades in opposed engagement with the coatedweb, the cariiages '12 aremoved horizontally along g'uide tracks 24 'onwhich they are slidably mounted. Movement ofthe carriages is,'in turn,controlled by the pneumatic piston-cylinder units 13 to which they areattached. Adjustable stop members are provided so that once a particularangular In addition to these polyurethane materials, such materials asNylon, Teflon and polyethylene having operating characteristicsequivalent to those of the polyurethane, as morefully described below,are suitable for use as metering blades in the present invention. Also,certain rubber materials may be suitable although generally rubber wouldnot have the same long wearing properties as polyurethane.

In constructing the metering blades for use in the coating system of thepresent invention, different angles of bevel ranging from 30 to 50 anddifferent thicknesses ranging from A to /2 inch have been foundsuitable. In FIG. 3, the presently preferred construction of apolyurethane blade having a durometer hardness of 95 Shore A is shown.The thickness of the blade is inch and the angle of bevel of the workingsurface is 40. In addition, the blade is provided with a back surface 27adjacent the leading edge of its working surface 26. This back surfacehas a total area which is a small fraction of the area of the workingsurface and is formed by tapering back the leading edge of the workingsurface at an angle of about or An alternative construction of the backsurface of the blade is shown in dotted lines in FIG. 3. Here the backsurface is divided into two segments 27' and 27". The particularconstruction chosen will depend mainly on the thickness of the blade.The creation of this back surface increases the thickness of the bladeat the leading edge of the working surface. thus lessening imperfectiondue to wear along this edge and improving the coating characteristics ofthe web. A blade having a working surface with a thin feathered edge. asopposed to the blunt tip construction shown in FIG. 3, may tend to betoo flexible and therefore non-responsive to pressure variations urgingthe blades against opposite sides of the web. Also, such thin edges onthe working surfaces of the opposed blades tend to vibrate as the web isfed therebetween and wear rapidly to produce a ragged contour and-thusan irregular coating pattern.

In fixing the opposed blades in opposed working operation, the angle ofextension of each blade, that is, the angle at which it extends from theblade holder as measured from the vertical path along which the webmoves, is set at a value greater than the angle of bevel of its workingsurface so as to effect an initial toe-to-toe engagement of the bladeswith opposite sides of the coated web. With the blade construction ofFIG. 3, the angles of extension ranging from about 40 to about 60 havebeen found suitable. Preferably, the amount of extension of the bladesis between inch and l /2 inches.

As shown in FIG. 4, the blades are urged toward each other with a forcesufficient to cause flexing thereof and to thus bring their workingsurfaces into at least a partially flush engagement with the oppositesides of the coated web. The amount of flexing is controlled by thesetting of the stops and the setting of the pressure exerted by the twopneumatic piston-cylinder devices 13. Suitable pressure settings forproducing the desired amount of flush contact of the blades with thecoated web have been found to range from about 8 to psi gauge. Thepressure exerted by the pneumatic piston-cylinder devices is in thehorizontal direction. Due to the flexing of the blades, however, as theyengage the opposite sides of the coated web, there is a component offorce produced which is in a direction extending along the path ofmovement of the web; and therefore, the resultant force acting on eitherside of the coated web is in a direction extending at an acute angle tothe path of movement of the web.

In setting the coating apparatus of the present invention for operation,there are two ultimate factors which can be varied by adjustment of theflexible opposed blade unit to vary the coat weight of the finalproduct, these being the area of flush contact of the working surfacesof the blades with the opposite sides of the coated paper and thepressure per unit area exerted by these working surfaces against theopposite sides of the paper. These two ultimate factors are, in turn,dependent on certain secondary characteristics of the blade unit, namelythe blade material, blade thickness, amount of blade extension, angle ofblade extension and air cylinder pressure provided by the units 13.

Generally, an increase in air cylinder pressure causes the opposedblades to deflect. This deflection brings the blade bevels fromtoe-to-toe position towards flush position and thus increases the areaof blade coming in contact with the web. The increase in air cylinderpressure tends to decrease the coat weight while the simultaneousincrease in surface area of the blade contact with the web tends toincrease coat weight. The actual coat weight obtained is the resultantof these two effects. When the flush position is reached, furtherincrease in pressure decreases the area of contact because it moves fromflush to a heel-to-heel contact and away from the toe. FIG. 6 shows theeffect of area of contact and pressure on the final coat weight of thepaper. The line ABC represents the drop in coat weight with increase inair cylinder pressure if the area of blade contact with the web wouldhave remained constant. The graph AEFG shows the increase in coat weightdue to increase in area of contact with the web if the air pressurewould have remained constant. AHJK represents the resultant curverepresenting the resultant coat weight against air pressure.

When the bevels of the blades approach a full flush position, the rateof increase in area of contact with the web increases at a higher ratethan a unit increase in air pressure and thus the curve AEFG isshallower first and it becomes increasingly steep. When the full flushposition is reached, the further increase in air pressure causes theblades to ride on the heel only with subsequent reduction in contactarea with the web and thus the graph PO is shown dropping back. The rateof decrease in coat weight due to increase in pressure remains constantwhile the rate of change in coat weight due to the change in contactarea of bevels does not remain constant, and thus the resultant curveAHJ K.

Thick blades or lower blade extension or higher head angles (i.e., anglebetween the head and the vertical web) or combinations of all threegives lower blade flexibility and the shape of the curve AEFG will bereplaced by curve ALMN, which is shallower for a wide range of airpressures and thus the new resultant coat weight decreases for a widerrange of pressures. Thinner blades, higher extensions and lower headangles tend to give the curve APQR in place of curve AEFG. In this case,the area of contact with paper increases very rapidly and the heels arereached at lower air pressures. In a coating operation, the blades maybe set anywhere between toe-to-toe and heel-to-heel relationship.Generally, with coating materials having higher solids content, lessarea of contact is required to produce a given coat weight. Here, theblades would near a toe-to-toe relationship. Conversely, with coatingshaving lower solids content, the opposed blades would be set nearer afull flush engagement with the opposite sides of the coated paper toproduce a given coat weight.

By selecting blades having particularly physical characteristics and byselecting different operating conditions for the blade unit, a widerange of coated products having coat weight characteristics superior tothe products of conventional coating apparatus can be produced. Inaddition, the coat weight of the final product can be varied by changingthe solids content of the coating material and the speed at which theweb is run through the opposed metering blades.

Representative results of tests run under various operating conditionsof the coating apparatus of the present invention are set out in TableII and Table III below. The coat weights are a measurement of thecoating on both sides of the paper and are given in pounds per bookpaper ream of 500 sheets of 25 inches X 38 inches. Also, the bladematerials in Table III are designated by letters S, M, H and PE; with Srepresenting the soft polyurethane 9O Shore A, M representing the mediumsoft polyurethane 95 Shore A, H representing the hard polyurethane ShoreD, and PE representing polyethylene.

Effect of Different Variables on Coat Weight With Two PolyurethaneBlades Having Same Durometer Hardness (95 Shore A) Blade Pressure (AirCylin- 7! Solid Web Speed in Blade Blade Angle of der Pressure) CoatWeight Variable Content Ft.Per.Min. Thickness Extension Extension inP.S.l.G. in lbs/ream Pressure 53.5 500 /4" 55 8 14.3 53.5 500 "/1" 4" 5511,9 53.5 500 4" 55 8,2 Pressure 53.5 500 At A" 47Vz 8 23.0 53.5 500 A1"A 47% 15 19,7 53.5 500 A" 47/ 30 15.9 Angle of Extension 53.6 500 A" 5012 12,7 53.6 500 A" A" 52/ 12 8,3 53.6 500 A" 55 12 7.9 Angle ofExtension 53.5 500 50 12 17,5 53,5 500 /s" A 52V2 12 13.1 53.5 500 4" 5512 10,3 Blade Thickness 53.5 500 /1" 54" 55 8 14,3 53.5 500 W 55 8 8.2Angle of Extension 53.5 500 /a" A" 55 8 14.3 53.5 500 A1" 47 /z 8 23.0Angle of Extension 53.4 500 /8" 1 55 8 10.5 53.4 500 l' 47% 8 20.7 WebSpeed 52.9 400 A" 47 13.4 52.9 600 A 47 18.8 52.9 800 A" 4" 47 23.4 WebSpeed 50.1 400 A" 1" 48 11.8 50.1 600 A 1'' 48 14.0 50.1 800 A" 1'' 4818.0

TABLE [II Effect of Different Variables on Coat Weight With DifferentCombinations of V4" Blade Materials Blade Pressure (Ai'r Cylin- %SolidWeb Speed in Blade Blade Angle of der Pressure) Coat Weight VariableContent Ft. Per Min. Material Extension Extension in P.S.l.G. inlbs/ream Angle of Extension 50.7 650 PE 1%" 44 18.4

M 1%" 45 50.7 650 PE 1%" 54 10.0

M 1%" 53 Length of Exten- 50.2 350 M 1%" 58 6.5 sion and Angle of S15/16" 54 Extension M 1%" 57 46.4 350 S 51 7.5 Length of Extension 535350 H 1%" 12.0 and Angle of Exten- S 47% sion 53.5 350 H /4" 50 9.4

S 53 Length of Extension 55.1 500 {PE 1%" 589?} 7 psig 16.4 Angle ofExtension S A" 57% and Pressure PE 1%" 59 30 psig 8.4

55.1 500 S 53 %Solid Content 56.1 500 S 56 15 psig 7.5 and Web Speed Sb" 55% 56.1 750 S k" 56 15 psig 10.1

S k" 55% Length of Extension 46.6 350 {H 1%" 58 7 psig 6.7 Angle ofExtension M 54% 46.6 350 H 1%" 525? 7 psig 8.3

As is seen from examination of the Tables 11 and 111, above, higher coatweights are obtained where a pair 0 polyurethane blades having adurometer hardness of 95 Shore A are used. Also, with such blades, thehigher coat weights are obtained by using the thicker inch blades with ablade extension of 182 inch; the lower blade pressures and the smallerangles of extension.

As is seen from Table 111, other blade combinations may also be usedalthough the coat weights of the final product are not as high.Generally, the control over the coat weight is affected by theflexibility of the blade unit. If the unit becomes too flexible, thepressure acting on opposite sides of the web cannot be properlyregulated. If, on the other hand, the blade unit becomes too stiff, itwill tend to produce an irregular coating because the loss offlexibility results in a loss in the metering and smoothing action ofthe blades on the coating. As indicated above, however, flexibility ofany particular blade is dependent on the thickness of the blade, theamount of blade extension and the head angle of the blade. Accordingly,in choosing the particular materials for the blades, these factors areto be considered in setting the blade unit so as to provide thenecessary flexibility for producing acceptable coated paper.

With the construction of the coating apparatus of the present invention,the quality of the coated paper for a given coat Wight and solidscontent is generally higher than that obtainable with presentlyavailable, conventional coating apparatus. The higher quality for agiven coat weight as obtainable with the opposed blade construction ofthe present invention has special significance, for example, in highopacity light weight grades of paper where the highest ratio of basesheet weight to coating is desired so as to maintain the highestpossible sheet strength and opacity.

With the flexible blade unit of the present invention, it is alsopossible to obtain higher and a greater range of coat weights for acoating material having a given solids content than with conventionalcoating methods. Not only may a wide variety of coating materials besatisfactorily used by the opposed blade construction of the presentinvention but also the flexible blade unit enables the apparatus to berun over a range of web speeds greater than is possible withconventional coaters while still maintaining a high quality coating.Also, the coating profile of the final product is enhanced due to thenon-rigid mounting of the blades in the blade holders.

In addition to the versatility of the coating apparatus of the presentinvention and the variety of the quality coated products which it iscapable of handling, the construction and physical properties of theopposed blades and the manner in which they are oriented relative toeach other as a working flexible unit, contribute to increasing the lifeof the individual blades over that of steel blades used in conventionalcoating systems. Also, the overall construction of the system providesan apparatus which is compact in size and efficient in operation.

The above description of the present invention has been made withparticular reference to the presently preferred embodiment; however, itis to be understood that various changes thereto may be made withoutdeparting from the scope of the invention as set forth in the followingclaims.

I claim:

1. The method of simultaneously coating the opposite sides of a paperweb comprising the steps of:

a. applying a layer of coating material to the opposite sides of theweb;

b. feeding said coated web along a predetermined path;

c. engaging said coated web, as it moves along said predetermined path,by a pair of flexible metering blades disposed and aligned on oppositesides of the web, each said blade extending freely at an acute anglerelative to the plane of the coated web in the direction from which thecoated web is approaching the blades, each said blade having a generallyflat beveled working face where it engages the coated web; and

d. simultaneously applying equal and opposed pressure against alignedopposite sides of the coated web over an area defined by the width ofthe web and a distance along its length as it moves along saidpredetermined path by urging said blades toward each other with a forcesufficient to establish and maintain at least a partially flushengagement of said working faces with the opposite sides of the coatedweb.

2. The method of coating a paper web as defined in claim 1 furthercharacterized by applying said pressure against the aligned oppositesides of said coated web in a direction urging said web along its pathof movement.

3. The method of coating a paper web as defined in claim 2 furthercharacterized by feeding said web along a predetermined path extendingin a vertically upward direction after said layer of coating is appliedto the opposite sides thereof.

4. A process of coating a paper web wh ch Comprises moving a paper webwith web coating on each face through a path that includes a straightportion, and at that straight portion passing said web between yieldableopposed blades, one blade engaging and extending across one of thecoating-carrying surfaces, and the other blade engaging and extendingacross the other coating-carrying surface, each blade extending to alocation spaced from the surface it engages, and being held at thatlocation so that it is positioned for the web to approach it at an acuteangle, each blade having a generally flat beveled working face where itengages the coating-carrying web; pressing said blades against eachother on opposite sides of the coating-carrying web with a continuouslyapplied equal and opposed force sufficient to maintain said blades inflexed position and to maintain at least a partially flush engagement ofsaid working faces with the opposite sides of the coating-carrying webto meter and smooth the layer of coating carried by the opposite sidesof the web; and drying the smoothed coatings on the web.

5. A process according to claim 4 further characterized by moving theweb with wet coating material on each face in an upward, verticaldirection through the straight portion of said path.

6. A process according to claim 4 further characterized by moving theweb with wet coating material on each face at a speed in the range offrom below 600 ft. per minute to above 1,400 ft. per minute.

7. A process according to claim 4 further characterized by moving theweb with wet coating material on each face between flexible plasticblades each of which is of the order of about A to about /2 inch inthickness and is tapered back at the rearward edge of said working faceat an angle to form a blunt tip.

8. A process according to claim 4 further characterized by moving theweb with wet coating material on each face at a speed in excess of 1,400ft. per minute.

9. A process according to claim 4 further characterized by moving theweb with wet coating material on each face at a speed below 600 ft. perminute.

10. The method of simultaneously coating the opposite sides of a paperweb comprising the steps of a. moving the web in a predetermined paththat includes a vertical, straight portion in which the web moves in anupward direction;

b. in a lower region of said straight portion applying to andestablishing on each of the opposite sides of the upwardly moving web alayer of wet coating material;

c. in a higher region of said straight portion simultaneously applyingequal and opposed pressure against aligned opposite layercontainingsides of the upwardly moving coated web by passing the coated webbetween the rectangular nip of a pair of opposed downwardly extendingflexed blades with beveled working surfaces pressed toward each otherand extending across the width of the web;

and

d. in a still higher region of said straight portion drying theresulting smooth coatings on the web.

surface at an angle to form a back surface of an area equal to a smallfraction of the area of said working surface.

14. The method of claim 10 wherein the blades are constructed of plasticmaterial having a hardness value of between about 90 Shore A and ShoreD.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO.3,889,018

DATED 1 June 10, 1975 INVENTOR(S): Lawrence H. Shepherd, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 5, line +2, shins 18," should read shims l8, Column 9, line 59,"182 inch" should read 5/4 inch Column 10, line 67, "Wight" should readweight Column 12, line 7 (Claim t), "coating on" should read coatingmaterial on Signed and Scaled this tenth Day of February 1976 [SEAL]Arrest:

RUTH. C. MIAHSON C. MARSHALL DANN 011w" Commissioner uj'Parents andTrademarks PATENT NO.

DATED INVENTOR(S) 1 UNITED STATES PATENT OFFICE CE'HFICATE 0F CORRECTIONJune 10, 1975 Richard J. Quint It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 5, line i2, shims l8,

3/4 inch weight read coat Column 9, line 59, Column 10, line 67,

"shins 18," should read "182 inch" should read "Wight" should readColumn 12, line 7 Claim i) "coating on" should ing material on Thiscertificate supersedes Certificate of Correction issued February 10,1976.

[SEAL] A ttest:

RUTH C. MASON A nesting ()jficer Signed and Sealed this eighteenth Dayof May 1976

1. The method of simultaneously coating the opposite sides of a paper web comprising the steps of: a. applying a layer of coating material to the opposite sides of the web; b. feeding said coated web along a predetermined path; c. engaging said coated web, as it moves along said predetermined path, by a pair of flexible metering blades disposed and aligned on opposite sides of the web, each said blade extending freely at an acute angle relative to the plane of the coated web in the direction from which the coated web is approaching the the blades, each said blade having a generally flat beveled working face where it engages the coated web; and d. simultaneously applying equal and opposed pressure against aligned opposite sides of the coated web over an area defined by the width of the web and a distance along its length as it moves along said predetermined path by urging said blades toward each other with a force sufficient to establish and maintain at least a partially flush engagement of said working faces with the opposite sides of the coated web.
 2. The method of coating a paper web as defined in claim 1 further characterized by applying said pressure against the aligned opposite sides of said coated web in a direction urging said web along its path of movement.
 3. The method of coating a paper web as defined in claim 2 further characterized by feeding said web along a predetermined path extending in a vertically upward direction after said layer of coating is applied to the opposite sides thereof.
 4. A process of coating a paper web which comprises moving a paper web with web coating on each face through a path that includes a straight portion, and at that straight portion passing said web between yieldable opposed blades, one blade engaging and extending across one of the coating-carrying surfaces, and the other blade engaging and extending across the other coating-carrying surface, each blade extending to a location spaced from the surface it engages, and being held at that location so that it is positioned for the web to approach it at an acute angle, each blade having a generally flat beveled working face where it engages the coatingcarrying web; pressing said blades against each other on opposite sides of the coating-carrying web with a continuously applied equal and opposed force sufficient to maintain said blades in flexed position and to maintain at least a partially flush engagement of said working faces with the opposite sides of the coating-carrying web to meter and smooth the layer of coating carried by the opposite sides of the web; and drying the smoothed coatings on the web.
 5. A process according to claim 4 further characterized by moving the web with wet coating material on each face in an upward, vertical direction through the straight portion of said path.
 6. A process according to claim 4 further characterized by moving the web with wet coating material on each face at a speed in the range of from below 600 ft. per minute to above 1,400 ft. per minute.
 7. A process according to claim 4 further characterized by moving the web with wet coating material on each face between flexible plastic blades each of which is of the order of about 1/4 to about 1/2 inch in thickness and is tApered back at the rearward edge of said working face at an angle to form a blunt tip.
 8. A process according to claim 4 further characterized by moving the web with wet coating material on each face at a speed in excess of 1,400 ft. per minute.
 9. A process according to claim 4 further characterized by moving the web with wet coating material on each face at a speed below 600 ft. per minute.
 10. The method of simultaneously coating the opposite sides of a paper web comprising the steps of a. moving the web in a predetermined path that includes a vertical, straight portion in which the web moves in an upward direction; b. in a lower region of said straight portion applying to and establishing on each of the opposite sides of the upwardly moving web a layer of wet coating material; c. in a higher region of said straight portion simultaneously applying equal and opposed pressure against aligned opposite layercontaining sides of the upwardly moving coated web by passing the coated web between the rectangular nip of a pair of opposed downwardly extending flexed blades with beveled working surfaces pressed toward each other and extending across the width of the web; and d. in a still higher region of said straight portion drying the resulting smooth coatings on the web.
 11. The method of claim 10 further characterized by moving the web at a speed in excess of 1,400 ft. per minute.
 12. The method of claim 10 further characterized by moving the web at a speed below 600 ft. per minute.
 13. The method of claim 10 wherein each blade is tapered back at the upper edge of said beveled working surface at an angle to form a back surface of an area equal to a small fraction of the area of said working surface.
 14. The method of claim 10 wherein the blades are constructed of plastic material having a hardness value of between about 90 Shore A and 70 Shore D. 